Evidence That the Angiotensin IV (AT4) Receptor Is the Enzyme Insulin-regulated Aminopeptidase

Abstract

Central infusion of angiotensin IV or its more stable analogues facilitates memory retention and retrieval in normal animals and reverses amnesia induced by scopolamine or by bilateral perforant pathway lesions. These peptides bind with high affinity and specificity to a novel binding site designated the angiotensin AT 4 receptor. Until now, the AT 4 receptor has eluded molecular characterization. Here we identify the AT 4 Central infusions of the hexapeptide VYIHPF (angiotensin IV, Ang IV) 1 or its more stable analogues, Nle 1 -Ang IV andNorleucinal Ang IV, facilitate memory retention and retrieval in rats in the passive avoidance and Morris water maze paradigms (1-3). In two rat models of amnesia, induced by the muscarinic antagonist, scopolamine, or bilateral perforant pathway lesion, the Ang IV analogues reversed the memory deficits detected utilizing the Morris water maze paradigm (3, 4). Enhancement of long term memory by Ang IV has also been demonstrated in species as distant as crabs (5). Angiotensin IV and its analogues enhance long term potentiation in both the dentate gyrus in vivo (6) and the CA1 region of the hippocampus in vitro (7), possibly via actions at the post-synaptic terminal. We have also shown that Ang IV enhances K ϩ -evoked acetylcholine release from rat hippocampal slices (8).The actions of Ang IV and its analogues are mediated by the angiotensin AT 4 receptor, defined by an international nomenclature committee (9) as the high affinity binding site specific for Ang IV (10). The AT 4 receptor has since been shown to bind with nanomolar affinity the decapeptide, LVVYPWTQRF (LVV-H7), isolated from sheep cerebral cortex (19).Although first identified in bovine adrenal, the receptor is widely distributed throughout the brain and peripheral organs (11). In the central nervous system, its distribution is highly conserved in guinea pig (12), macaque monkey (13), and human (14) brains. AT 4 receptors occur in high levels in the basal nucleus of Meynert, in the CA1 to CA3 regions of Ammon's horn in the hippocampus, and throughout the neocortex, areas important for cognitive processing. Despite the dramatic central effects of Ang IV and the abundance of the receptor in the central nervous system, the identity of the AT 4 receptor and the mechanism by which its ligands mediate their actions were unknown. MATERIALS AND METHODSProtein Purification-AT 4 receptors in bovine adrenal membranes (16 mg of membrane protein) were cross-linked to the photoactivatable analogue of Ang IV, [ 125 I]Nle 1 -BzPhe 6 -Gly 7 -Ang IV as described previously (15). Cross-linked membranes were solubilized in solubilization buffer (1% CHAPS, 20 mM Tris-HCl, pH 7.5, 5 mM EDTA) with shaking at room temperature for 48 h, and insoluble material was pelleted by centrifugation at 100,000 ϫ g for 1 h at 4°C. Non-cross-linked membranes (48 mg of protein) were solubilized and centrifuged similarly, and the supernatant was combined with that from cross-linked membranes. Solubilized membrane proteins were applied to a 1-ml DEAE fas...

Human Leukocyte-derived Arginine Aminopeptidase

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Renin-Angiotensin-Aldosterone System and Progression of Renal Disease

“…AngIV binds to a specific receptor called AT 4 , which is widely expressed in the kidney, including endothelial cells and proximal as well as convoluted tubules. The AT 4 receptor, by protein purification and peptide sequencing, has been identified to be insulin-regulated aminopeptidase (11).…”

Identification of a Tankyrase-binding Motif Shared by IRAP, TAB182, and Human TRF1 but Not Mouse TRF1

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